Want to get volume using 3dprint addon but get Problem From blender Console
Python NameError
The error occurs on this line.
bm = mesh_helpers.bmesh_copy_from_object(obj, apply_modifiers=True)
      

and is informing you that mesh_helpers is not defined.
Assume you are doing a bit of copy paste to and from the 3D print addon, where no doubt mesh_helpers is imported and available, whereas you missed it. It  can be imported from the 3D print toolbox
from object_print3d_utils import mesh_helpers

may find similar issues with clean_float and _scale.